The concept of a sheet-like recording medium is to be understood very widely in the present application. On the one hand it covers papers used in office equipment such as scanners, printers, copiers, as well as in cash separators and printing presses. On the other it covers the sphere of adhesively interconnected, laminated materials, particularly labels, splice, break or tear-off points. The term recording medium is also implied as covering foils and banknotes.
When processing such recording media or the corresponding laminated, flat objects in copiers or separating equipment, such as automatic teller machines, there is an absolute need for an individual supply of the recording media present in stacks for the purpose of further processing or discharge. Despite the high reliability of mechanical separating systems, a problem constantly arises of multiple withdrawals or no withdrawal. Therefore it is vital to avoid or at least detect multiple, double or missing sheets of such recording media.
The present application also considers flat objects to cover objects present in sheet form, such as paper, films, foils, plates, corrugated boards and other such materials or packs and multiply laminated materials adhesively applied to a base or support material, for example, labels, splice, break or tear-off points and the like.
As a corresponding method for the contactless detection of the recording media with a view to there being a separation or a single sheet is also to be usable over a wide gram weight or weight per unit area range of such recording media, significant problems arise in being able to very reliably implement this from technical and economic standpoints.
DE 36 20 042 A1 discloses a method and a device of the aforementioned type. In order to be able to achieve the high security and reliability in connection with detection and the corresponding information provided to the effect that there has been a separation of the corresponding recording medium and no multiple or missing sheet exists, the known device makes use of two sensor devices with in each case two transducers. When using ultrasonics there is both an amplitude evaluation and a phase evaluation. In this device the acting disturbance variables or the drift of the ultrasonic frequency are detected by the use of a second ultrasonic comparison measuring section and in a comparison circuit difference values are formed with the corresponding measuring values, which are taken into account in the detection statement. In the case of different paper weights a learning stage is firstly necessary.
Admittedly in this way the known method and device can take account of disturbance variables such as transducer drift, temperature drift, and transit time changes through ambient temperature. However, the detectable gram weights are in a relatively narrow range of, for example, 35 to 400 g/m2.
The known device and method are technically very complicated, without achieving a relatively high flexibility relative to a broad gram weight spectrum. Other methods and devices for detecting single sheets are, for example, known from DE 199 21 217 A1 and EP 1 067 053 A1. These ultrasonically based devices use sensor devices with a forked structure. For detecting labels it is necessary to have a preceding learning step, i.e., with respect to the label thicknesses expected in the detection process, so as to be able to pre-establish the corresponding specific signal values and ranges. These known devices have an excessively complex construction and can be strongly influenced by disturbance variables.
The detection of separated banknotes as disclosed, for example, in DE 102 33 052 A1 is also relatively complicated. It is assumed that radiation emanating from the banknote or recording medium is detected in at least two areas. If the banknote is present in multiple form, the measuring signal obtained through the radiation is significantly modified and attenuated, so that a detection criterion can be derived therefrom.